(1) Field of the Invention
The present invention relates to a method of producing a water-in-oil emulsion explosive (hereinafter, referred to as W/O emulsion explosive), and more particularly relates to a method of producing a W/O emulsion explosive, wherein a stable water-in-oil emulsion (hereinafter, referred to as W/O emulsion) is produced in a short time through a specifically limited emulsifying step, and the resulting W/O emulsion is kneaded together with hollow microspheres through a specifically limited kneading step, whereby the W/O emulsion and the hollow microspheres can be homogeneously kneaded in a short time without substantially causing breakage of the hollow microspheres.
(2) Description of the Prior Art
U.S. Pat. No. 4,138,281 specification discloses a method of producing W/O emulsion explosive comprising aqueous solution of inorganic oxidizer, oil, emulsifier and hollow microspheres. This method comprises five steps as illustrated in FIG. 1, that is, a step for conditioning an aqueous solution of inorganic oxidizer, a step for conditioning a mixture of oil and emulsifier, a step for emulsifying the mixture of oil and emulsifier together with the above described aqueous solution of inorganic oxidizer into a W/O emulsion, a step for kneading the resulting W/O emulsion together with hollow microspheres, and a step for packing the resulting W/O emulsion explosive. Among these steps, the emulsifying and kneading steps are most important. That is, whether a good W/O emulsion is obtained or not has a high influence upon the quality and storage stability of the resulting W/O emulsion explosive. The kneading step is carried out in order to disperse homogeneously hollow microspheres having a very small specific gravity into a W/O emulsion having a relatively large specific gravity, and whether a good dispersion is formed or not has a high influence upon the explosion property and other properties of the resulting W/O emulsion explosive.
However, the above described U.S. patent discloses the use of an ordinary continuous mixer in the emulsifying step, and the use of an ordinary continuous kneader in the kneading step, and does not disclose the use of a particular emulsifying machine and a particular kneader.
Moreover, the method described in the above described U.S. patent comprises a large number of steps, and therefore a long time is required for the production of W/O emulsion explosive, and the method is not desirable as a commercial method. In order to overcome this drawback, the inventors have already proposed in U.S. Pat. No. 4,410,378 a method of producing W/O emulsion explosive, wherein emulsification and kneading are carried out in one step.
That is, U.S. Pat. No. 4,410,378 discloses a method of producing a W/O emulsion explosive, wherein hollow microspheres, and a mixture of aqueous solution of inorganic oxidizer, oil and emulsifier are separately supplied into a common passage; the hollow microspheres and the mixture of the aqueous solution of inorganic oxidizer, the oil and the emulsifier are emulsified and kneaded on the surface of a disc, which is arranged on the downstream side of the passage and has projections, while rotating the disc; the emulsified and kneaded mixture is flowed down from the outer peripheral portion of the disc into a kneading room formed under the disc, while continuing the emulsification and kneading; and emulsified and kneaded mixture is taken out from the kneading room.
Although the method of U.S. Pat. No. 4,410,378 can produce W/O emulsion explosive in a very short time, the method still has problems to be solved that, due to the concurrent emulsification and kneading, a high shear force acts on hollow microspheres, and some kinds of hollow microspheres, for example, shirasu hollow microspheres (shirasu is a kind of volcanic ash) and the like are broken in a large amount during the emulsifying and kneading step, and the resulting W/O emulsion explosive is poor in the quality and in the explosion performance.
The inventors have made various investigations in order to solve this problem, and have found that, when the emulsifying and kneading machine used in the above described emulsifying and kneading step is used as an emulsifying machine in an emulsifying step and is connected to a specifically limited kneading machine used in a kneading step following to the above emulsifying step, the breakage of hollow microspheres can be noticeably decreased and a W/O emulsion explosive can be obtained in a short time. As the result, the present invention has been accomplished.